JP2530007B2 - Ground fault overvoltage relay - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a ground fault overvoltage relay.

B. SUMMARY OF THE INVENTION The present invention is a ground fault overvoltage relay that takes in a phase voltage from a secondary circuit of a transformer for an instrument and detects a ground fault from a zero phase voltage derived from the phase voltage. When the two phases are below a certain value,
Alternatively, when the ratio between the minimum line voltage and the minimum phase voltage is more than a specified value, it is judged as an abnormality of the instrument transformer and the relay output is locked to detect the ground fault with high sensitivity and the abnormality of the transformer. It is possible to prevent malfunctions and malfunctions due to.

C. Conventional technology There are various protective relays that protect the power system, but ground fault overvoltage relays are often used to detect ground faults in the resistance ground system. This ground fault overvoltage relay detects a system ground fault from the zero-phase voltage generated at the time of a system fault.

A conventional ground fault overvoltage relay has two
The street type is known. In the figure, a transformer 2 for instruments is connected to a three-phase power system line 1, and a ground fault overvoltage relay 3 for detecting a ground fault from an output of a secondary circuit of the transformer 2 or a tertiary circuit of the transformer 2. A ground fault overvoltage relay 4 that detects from the output is provided.

The ground fault overvoltage relay 3 takes out the voltages V ₁ , V ₂ and V ₃ with respect to the neutral point potential V ₄ of the secondary circuit (star connection) of the transformer ₂ by the input transformers 3 ₁ , 3 ₂ and 3 ₃ , respectively. Each of these transformers 3 ₁ , 3 ₂ , 3, ₃
Synthesizing circuit 3 the output of the ₄ detects the zero-phase voltage V ₀ by combining with, ground fault detection by determining whether the zero-phase voltage V ₀ is above set point K in the determination circuit ₃₅ And get its protection output.

Ground fault over voltage relay 4 takes the input transformer 4 ₁ zero-phase voltage voltage V ₅ -V ₆ of the 3 primary circuit of the transformer 2 (delta connection), the zero-phase voltage V ₀ to be the output of the transformer 4 ₁ Judgment circuit
4 Judgment in ₂ to obtain protection output.

D. Problem to be Solved by the Invention In the conventional ground fault overvoltage relay 4, when a disconnection or a short circuit occurs in the tertiary circuit of the transformer ₂ , the input zero-phase voltage V _{0 of the} determination circuit 4 ₂
Becomes almost zero. In this state, when the ground fault of the system line 1 occurs, the system outputs the determination output of the system normal regardless of the zero-phase voltage generated on the line side, and there is a problem that the relay 4 malfunctions.

At this point, in the ground fault overvoltage relay 3, an apparent zero-phase voltage V ₀ is generated even when the secondary circuit of the transformer 2 is disconnected, short-circuited, or a ground fault occurs. It is intended to detect and prevent a malfunction at the time of an actual power system accident.

Here, the apparent zero-phase voltage V ₀ due to the abnormality of the secondary circuit of the transformer 2 is as described below.

(A) When there is no line load in the secondary circuit, the apparent zero-phase voltage V ₀ when one phase (for example, a phase) of the secondary circuit becomes = 0 and is | V ₀ | = | _a + _b + _c | = e, and the constant voltage e of the secondary circuit (generally become.

(B) If the secondary circuit has a line-to-line load, the a phase is disconnected.
The voltage V ₀ when _a = _x is | V ₀ | = | _a + _b + _c | = e + α where α is in the following range determined by the impedance ratio between the line load and the a-phase load.

With respect to the zero-phase voltage V ₀ as described above, the sensitivity (setting value K) of the ground fault overvoltage relay 3 is selected to be 30 to 40% of the zero-phase voltage generated when the system 1 line has a complete ground fault. Then, the voltage input from the secondary circuit to the relay 3 at the time of one-line complete ground fault is designed to be three times the secondary circuit rated voltage (e × 3 = 190V). Therefore, the set value K of the relay 3 is set to about 57 to 76V.

In such a configuration, if there is no line load in the above item (a), the relationship of the settling K> zero-phase voltage V ₀ due to the secondary circuit abnormality> the detection level of the secondary circuit abnormality is maintained, It is possible to realize a relay that distinguishes between detection of a secondary circuit abnormality and detection of an actual system accident.

However, when there is a line load in the above item (b), the apparent zero-phase voltage generated by the secondary circuit abnormality is V ₀ as shown in FIG. 9 in the case of the a-phase abnormality. It also becomes. In order to prevent the relay 3 from malfunctioning even with this voltage, it is necessary to set the set value K to 110 V or higher. At this time, the settling value K becomes about 60% (= 190V / 110V) of the zero-phase voltage V ₀ generated at the time of complete ground fault between system 1 lines, which is much higher than the original target sensitivity of 30-40%. It may become impossible to detect depending on the system accident situation.

E. Means for Solving the Problems The present invention has been made in view of the above-mentioned problems, and detects the zero-phase voltage by combining the secondary circuit outputs of the instrument transformer and detects the zero-phase voltage. In a ground fault overvoltage relay that detects a ground fault of a power system by comparison with a set value, first detecting that at least two phases of a line voltage are below a predetermined value.
And a second determining unit that detects that the ratio of the minimum line voltage to the minimum phase voltage is less than or equal to a predetermined value, and the ground fault overvoltage when at least one of the determining units has a detection output. Locking means for locking the detection output.

F. Action FIG. 5 shows that the ground fault overvoltage relay 3 is connected to the secondary circuit of the transformer 2 with its input impedances Z _a , Z _b and Z _c , and in parallel with it the impedances Z _ab and Z _bc. , Z _ca Δ load 5 is connected. In this configuration, when the transformer 2 has a disconnection of the primary circuit (for example, point A) or a disconnection of the secondary circuit (for example, point B), among the input voltage vectors _{a 1} , _b , and _c of the relay 3, the disconnection phase a the voltage vector _a limited inside the circle O _1, O _2, O ₃ shown in Figure 6.
The circle O ₁ ... has AB as its diameter and is determined from Z _ca , Z _bc = ∞ Z _ab = resistance component Z _a = reactance component. In the circle O ₂ , Z _ab , Z _bc = ∞ Z _ca = reactance component Z _a = resistance component, and in the circle O ₃ , Z _a = ∞ Z _ca = reactance component (or resistance component) Z _ab = resistance component ( Or reactance component).

For a voltage _a limited to the above range, the input voltage vector to the relay 3 when the transformer 2 is in the normal state is shown in FIG. 7 (A) when the power system line 1 is normal, and the a-phase 1-line ground fault is shown. FIG. 7 (B) sometimes shows the case where the arc resistance can be ignored in the case of the ab phase two-wire ground fault, and FIG. 7 (D) shows the case where the arc resistance exists. As shown in FIGS. 7 (A) and 7 (B), the voltage vectors _{a 1} , _{b 2} , and _{c 3} are normal triangles DEF when the line 1 is normal or when the line 1 is grounded.
Come to the top. Therefore, the line voltages _ab , _ac , and _ca always maintain the rated voltage when the system is normal or when there is a one-line ground fault. Next, as shown in FIGS. 7 (C) and (D), at least two phases ( _bc , _{ca in the} figure) of the line voltages _ab , _bc , _ca maintain a certain level of voltage during a two-line ground fault. .

From the above, according to the present invention, the first determination unit that detects that at least two phases of the line voltage are equal to or less than the predetermined value, and the minimum line voltage to phase voltage ratio is equal to or less than the predetermined value. The abnormality of the transformer is determined by having a detection output in at least one of the second determination unit that detects the voltage, and the output of the relay 3 is locked by this determination. This prevents the erroneous protection output due to the abnormality of the transformer 2, while setting the sensitivity (30-40%) required for system protection in the relay 3,
In addition, malfunctions due to abnormalities in the transformer are prevented.

G. Embodiment FIG. 1 is a circuit diagram showing an embodiment of the present invention, showing only the abnormality detecting portion of the transformer. The first determination unit 11 determines the line voltages _ab , _bc , and _ca between the line voltages _ab ,
The maximum value (absolute value) max of _bc and _ca max {| _ab |, | _bc |, | _ca |} multiplied by a coefficient α (<1) and the maximum value max {of the constant K ₁ The determination circuits 11 ₁ , 11 ₂ , and 11 ₃ determine whether or not K ₁ , max {| _ab |, | _bc |, | _ca |} × α}. The outputs of the decision circuits 11 ₁ , 11 ₂ and 11 ₃ are gate 1
By 1 _{4-11 7} determines that there line voltage _{ab, bc,} the following at least two phases is a value of _ca, the determination output is abnormal determination output of the transformer 2. For example, the a-phase abnormality of the transformer 2, becomes a voltage V _a is limited to the range of O _1, O _2, O ₃ shown in FIG. 6, line voltage _ab of this time, _ca is the line voltage _bc It also becomes smaller. On the other hand, when the system line 1 is normal, at least two-phase line voltages _bc and _{ca in} the one-line ground fault and the two-line ground fault are maintained at values close to the line voltage _bc . Therefore, the value obtained by multiplying the line voltages _ab , _bc , _ca by the coefficient α corresponds to the minimum value of the transformer 2 in a normal state, and when at least two phases are smaller than this value, it can be determined that the transformer is abnormal. The coefficient α at this time is set so that the one-line ground fault does not malfunction, the two-line ground fault reduces the false lock region, and the abnormality of the transformer widens the detection region as much as possible. α is set to 0.75. This α
The detection area of transformer abnormality due to the setting of
It becomes the area shown in the figure.

The constant K ₁ is a fixed value for detecting the 2-wire disconnection of the transformer 2.

Next, the second determination unit 12 determines the line voltages _ab , _bc , _ca.
Minimum value (absolute value) min {| _ab |, | _bc |, | _ca |} and the minimum value (absolute value) min {| _a |, | _b | of phase voltages _a , _b , _c , | _C |} is smaller than a predetermined value β (> 1), that is, The determination by the determination circuit 12 _1, the phase voltage _{a, b,} the minimum of _c (absolute value) is greater than the constant K _2, i.e. _{min {| a |, | b} |, | c |} ≧ The determination circuit 12 ₂ determines K ₂ and the gate 12 ₃ determines that the outputs of both determination circuits 12 ₁ and 12 ₂ are simultaneously established, and the abnormality determination output of the transformer 2 is obtained. For example, the a-phase abnormality of the transformer 2 becomes the voltage V _a of the range shown in FIG. 6, the voltage _b that also includes this voltage _a,
The ratio of the minimum values of the line voltages _ab , _bc , _{ca to c} can take values with 1 as the boundary, but as is clear from FIGS. 7 (A) to (D) when the system line is normal and abnormal. , The minimum value of the phase voltages _a , _b , _c and the line voltage _ab , _bc ,
The ratio of the minimum value of _ca is That's all.

Therefore, if the ratio is equal to or less than a certain value β (eg β = 1.3), it can be determined that the transformer is abnormal. For this judgment,
The determination circuit 12 ₂ determines that the minimum value of the phase voltages _{a 1} , _{b 2} and _c is a constant K ₂ or more and sets the condition as a transformer abnormality determination condition, thereby preventing an erroneous determination in the determination circuit 12 ₁ . The coefficient β
Is the same as the above-mentioned α, the malfunction prevention by the one-line ground fault and the
The value is set to widen the detection area as much as possible for the reduction of the false lock area due to the line ground fault and the abnormal transformer. The detection area of transformer abnormality due to the setting of β is the third when β = 1.3.
It becomes the area shown in the figure.

Next, the judgment outputs of the judgment units 11 and 12 are logically ORed by the OR circuit 13, and when at least one of the judgment outputs of both judgment units is established, the output lock command of the ground fault overvoltage relay and the abnormality of the transformer are detected. Output as an alarm. This prevents erroneous system protection operation due to transformer abnormality, and eliminates malfunction of system protection due to early removal of transformer abnormality. The region for judging abnormalities in the transformer is the region shown in FIG. 4 which is a combination of the regions shown in FIGS. 2 and 3.

H. Effect of the Invention As described above, according to the present invention, the output of the ground fault overvoltage relay is determined by determining the transformer abnormality from the decrease in the line voltage of at least two phases and the pulling of the minimum phase voltage and the line voltage. Since it is locked, there is an effect that it is possible to almost certainly prevent malfunction due to abnormal transformer without lowering the sensitivity of the relay.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG.
3 is a vector diagram showing an example of a detection area of the determination unit 11 in the figure, FIG. 3 is a vector diagram showing an example of a detection area of the determination section 12 in FIG. 1, and FIG. 4 is a vector diagram showing an output area example of FIG. Fig. 5 is a connection circuit diagram of the transformer and the ground fault overvoltage relay, and Fig. 6 is the voltage V _a due to the disconnection of the transformer in Fig. 5.
Fig. 7 (A) is a vector diagram when the system is normal, Fig. 7 (B) is a vector diagram when one-line ground fault occurs, Fig. 7 (C) and Fig. 7 (D). ) Is a vector diagram at the time of 2-line ground fault, FIG. 8 is a conventional relay circuit diagram, and FIG. 9 is a zero-phase voltage vector diagram at the time of 1-line complete ground fault. 11 ... Judgment section, 11 ₁ , 11 ₂ , 11 ₃ ...... Judgment circuit, 12 ...... Judgment section, 12 ₁ , 12 ₂ , ... Judgment circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (73) Patent holder 999999999 Mitsubishi Electric Corporation 2-3-3 Marunouchi, Chiyoda-ku, Tokyo (73) Patent holder 999999999 Meidensha Co., Ltd. 2-1-117 Osaki, Shinagawa-ku, Tokyo (72) Inventor Yoshifumi Oura 1-3-3 Uchisaiwaicho, Chiyoda-ku, Tokyo Within Tokyo Electric Power Company (72) Inventor Kazuyoshi Yoshida 1-3-1, Uchisaiwaicho, Chiyoda-ku, Tokyo Within Tokyo Electric Power Company (72) Inventor Eijiro Ibaraki 1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd. (72) Inventor Yasuhiro Kurosawa No. 1 Toshiba-cho, Fuchu-shi, Tokyo Inside Toshiba Fuchu factory (72) Inventor Minoru Seya 1-1-1 Kokubun-cho, Hitachi-shi, Ibaraki Inside the Kokubun factory of Hitachi, Ltd. (72) Inventor Toshiki Hattori Wa, Hyogo-ku, Kobe-shi, Hyogo Sakimachi 1-chome No. 1 No. 2 Mitsubishi Electric Corporation control in the Works (72) inventor Toshiro Fujimoto Shinagawa-ku, Tokyo Gotanda 5-chome No. 5 No. 5 Co., Ltd. Meidensha Gotanda in the office

Claims (1)

(57) [Claims] 1. A ground fault overvoltage relay which takes in a phase voltage from a secondary circuit of a transformer for an instrument connected to a power system and detects a ground fault by the magnitude of a zero phase voltage by combining the phase voltages. At least 2 of the line voltage obtained from the phase voltage
A first determination unit that detects that the phase is less than or equal to a predetermined value,
When a second determination unit that detects that the ratio between the minimum value of the line voltage and the minimum value of the phase voltage is equal to or less than a predetermined value, and the first or second determination unit has a detection output A ground fault overvoltage relay, comprising: a lock unit that locks a ground fault detection output.